1. Field of the Invention
The present invention relates to a resin multilayer device including a balun (balance-unbalance transformer) for use in a wireless circuit and the like. Specifically, the present invention relates to a resin multilayer device including a stack-type balun formed by use of the Wafer Level Chip Size/Scale Package (WLCSP) technology.
2. Description of the Related Art
All patents, patent applications, patent publications, scientific articles, and the like, which will hereinafter be cited or identified in the present application, will hereby be incorporated by reference in their entirety in order to describe more fully the state of the art to which the present invention pertains.
Baluns are circuits in which two balanced signal transmission lines and one unbalanced signal transmission line are arranged in proximity via a dielectric layer to produce electromagnetic coupling between the balanced signal transmission lines and the unbalanced signal transmission line. Baluns convert unbalanced signals (single-ended signals) that have been input to the unbalanced signal transmission line into balanced signals (differential signals), and outputs them from the balanced signal transmission lines. Alternatively, in a manner reverse to this, baluns convert balanced signals that have been input to the balanced signal transmission lines into unbalanced signals and outputs them from the unbalanced signal transmission line.
A first end of the unbalanced signal transmission line is an input/output end for unbalanced signals (single-ended signals), and a second end of it is an open end. First ends of the two balanced signal transmission lines are input/output ends for balanced signals (differential signals), and second ends of them are ground ends, which are connected to the GND.
Stack-type baluns have a configuration in which an unbalanced signal transmission line and two balanced signal transmission lines are stacked via an insulative layer or a dielectric layer. Manufacturing methods of stack-type balun apparatuses include one based on the Low Temperature Co-fired Ceramics (LTCC) technique (for example, see Patent Documents 1 to 3), one based on the manufacturing method of multilayer printed wiring boards (for example, see Patent Document 4), one based on the semiconductor process technology (for example, see Patent Document 5, and Non-Patent Document 1), and one using a resin layer as a dielectric layer (for example, see Patent Documents 6 and 7).
Baluns also function as transformers for converting impedance. For impedance conversion, they are required to be designed so that the input impedance value on the unbalanced signal side (the single-ended signal input side) and the output impedance value on the balanced signal side (the differential signal output side) have a predetermined relationship. As representative values, the input impedance value on the unbalanced signal side (the single-ended signal input side) is 50Ω, and the output impedance value on the balanced signal side (the differential signal output side) is 50Ω, 100Ω, 150Ω, 200Ω or the like.
Parameters for satisfying these impedance specifications are: a width of the transmission lines; a thickness of the transmission lines; a thickness of the insulative layer between the transmission lines (namely, a distance between the transmission lines) and its dielectric constant; a thickness and a dielectric constant of the insulative layer on the lower side of the lower transmission line; and a thickness and a dielectric constant of the insulative layer on the upper side of the upper transmission line (for example, see Patent Document 4).
On the other hand, in these years, a technique called Wafer Level Chip Size/Scale Package (WLCSP) has been proposed (for example, see Patent Documents 8 to 10). The WLCSP is a technology in which a redistribution layer is formed on a wafer by the resin layer formation process and the fabrication process of thick-film Cu interconnection lines or other interconnection lines, followed by dicing into chips. Namely, it is a manufacturing method covering the steps to packaging while chips are in the wafer form. Note that the package manufactured by the WLCSP technology is called a Wafer Level Package (WLP).